A three-state model of resonance and its optical analogues. credit: nature (2023). DOI: 10.1038/s41586-022-05635-8
If she hits the right pitch, the singer can smash a wine glass. The reason is resonance. While glass may vibrate slightly in response to most acoustic tones, a tone that resonates with the natural frequency of the material itself can send its vibrations into overdrive, causing the glass to shatter.
Resonance also occurs on a much smaller scale than atoms and particles. When particles interact chemically, it is partly because certain conditions resonate with the particles in a way that prompts them to chemically bond. But atoms and molecules are constantly in motion, living in a blur of states of vibration and rotation. Picking out the exact resonance state that ultimately gives rise to the molecules’ interaction was nearly impossible.
MIT physicists may have unlocked part of this mystery with a new study appearing in the journal nature. The team reported that they first observed A echo in collision very cold particles.
They found that a cloud of supercooled sodium and lithium particles disappeared 100 times faster than normal when exposed to a very specific magnetic field. The rapid disappearance of the particles is a sign that the magnetic field is setting the particles into resonance, causing them to react more quickly than normal.
The results shed light on the mysterious forces that drive molecules to interact chemically. They also suggest that scientists could one day harness the natural resonance of particles to direct and control certain particles chimical interaction.
Study author Wolfgang Ketterle, MIT Professor of Physics, John D. “There have been suggestions that the molecules are so complex that they are like a dense forest, where you wouldn’t be able to recognize a single echo. But we did find one large tree that stood out, by a factor of 100. We noticed something completely unexpected.”
Ketterle’s co-authors include lead author and MIT graduate student Juliana Park, graduate student Yu Kun Low, former MIT postdoctoral researcher Alan Jamieson, now at the University of Waterloo, and Timur Chirpole at the University of Nevada.
Within a cloud of particles, collisions are constantly occurring. Molecules may sway together like overheating billiard balls or stick together in a brief but crucial state known as an “intermediate compound” which then triggers a reaction to transform the particles into a new chemical structure.
“When two molecules collide, most of the time they don’t reach that intermediate state,” says Jamieson. “But when they have resonance, the rate of going into that state goes up exponentially.”
“The intermediate compound is the mystery behind all chemistry,” Ketterle adds. “Usually the reactants and products of a chemical reaction are known, but not how one leads to the other. Knowing something about the resonance of molecules can give us a fingerprint of this mysterious middle state.”
Ketterle’s group looked for signs of resonance in atoms and molecules that are supercooled, to temperatures just above absolute zero. Such extremely cold conditions prevent the temperature-driven random motion of particles, giving scientists a better chance of identifying any more subtle signs of resonance.
In 1998, Ketterle made the first ever observation of such echoes in a very cold atoms. Note that when a very specific magnetic field was applied to the supercooled sodium atoms, the field enhanced the way the atoms scatter each other, in an effect known as the Feshbach resonance. Since then, he and others have searched for similar resonances in collisions involving both atoms and molecules.
“Molecules are much more complex than atoms,” says Ketterle. “They have many different states of vibration and rotation. Therefore, it wasn’t clear if the particles would show resonance at all.”
A needle in a haystack
Several years ago, Jamieson, who at the time was a postdoctoral researcher in Ketterell’s lab, proposed a similar experiment to see if signs of resonance could be observed in a mixture of atoms and molecules cooled to a millionth of a degree above absolute zero. by varying external magnetic fieldthey found that they could actually pick up many resonances between sodium atoms and sodium and lithium molecules, which I mentioned last year.
Then, as the team reports in the current study, graduate student Park took a closer look at the data.
“I discovered that one of those resonances does not involve atoms,” Ketterell says. “It blasted the atoms with laser light, and there was one resonance, very sharp, with nothing but particles.”
Park discovered that the particles seemed to disappear—a sign that the particles had undergone a chemical reaction—much more quickly than normal when exposed to a very specific magnetic field.
In their original experiment, Jamison and colleagues applied A magnetic field They varied widely up to 1000 Gaussians. Park discovered that the sodium-lithium particles suddenly disappeared, 100 times faster than normal, within a very small fraction of that magnetic range, at about 25 milligaussians. This is equivalent to the width of a human hair compared to a meter-long stick.
“It takes precise measurements to find the needle in that haystack,” says Park. “But we used a systematic strategy to amplify this new resonance.”
In the end, the team noticed a strong signal that this particular field resonates with the molecules. This effect enhanced the opportunity for the particles to bond into a short and medium complex which then led to a reaction that made the particles disappear.
Overall, the discovery provides a deeper understanding of molecular dynamics and chemistry. While the team doesn’t expect scientists to be able to induce resonance and direct reactions, at the level of organic chemistry, it may one day be possible to do so on a quantum scale.
“One of the main topics of quantum science is the study of systems of increasing complexity, especially where quantum control is close,” says John Doyle, a professor of physics at Harvard University, who was not involved in the group’s research. “This kind of resonance, first seen in simple atoms and then in more complex atoms, has given rise to amazing advances in atomic physics. Now that this has been shown in molecules, we must first understand it in detail, and then let the imagination run wild and think about what it might be.” Useful for building a larger supercooler particlesPerhaps an interesting case study.
Juliana Park, Feshbach resonances in collisions between triplet ground-state particles, nature (2023). DOI: 10.1038/s41586-022-05635-8. www.nature.com/articles/s41586-022-05635-8
Massachusetts Institute of Technology
the quote: Rare resonance in molecules first observed by physicists (2023, February 1) Retrieved February 1, 2023 from https://phys.org/news/2023-02-physicists-rare-resonance-molecules.html
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